Engine manufacturers have focused on improving engine design in order to improve fuel economy and efficiency (typically, based on Federal Corporate Average Fuel Economy (CAFE) standards) and reduce wear. Whilst improvements in engine design and operation have contributed, improved formulation of engine oil lubricant may also reduce wear whilst improving fuel economy and efficiency. They also serve to reduce the friction between sliding moving parts (typically metallic or ceramic) that are in contact.
It is well known for lubricating oils to contain a number of additives (including antiwear agents, antioxidants, dispersants, or detergents) used to protect internal combustion engines from wear, oxidation, soot deposits and acid build up. A common antiwear additive for engine lubricating oils is zinc dialkyldithiophosphate (ZDDP). It is believed that ZDDP antiwear additives protect the engine by forming a protective film on metal surfaces. ZDDP may have a detrimental impact on fuel economy and efficiency. Consequently, engine lubricants may also contain a friction modifier to obviate any detrimental impact of ZDDP on fuel economy and efficiency. Both ZDDP and friction modifier function by adsorption on sliding surfaces, and each may interfere with each other's respective functions.
Further, engine lubricants containing phosphorus compounds and sulphur have been shown to contribute in part to particulate emissions and emissions of other pollutants. In addition, sulphur and phosphorus tend to poison the catalysts used in catalytic converters, resulting in a reduction in performance of said catalysts.
With increasing control of emissions (typically to reduce NOx formation, SOx formation, formation of sulphated ash) there is a desire towards reduced amounts of sulphur, phosphorus and sulphated ash in engine oils. The phosphorus from ZDDP is also believed to be relatively volatile and with the coming introduction of the GF-5 specification, tighter limits on emissions of phosphorus may be required. However, reducing the levels of antiwear additives such as ZDDP is likely to increase wear and result in other detrimental performance of an engine.
In addition, as technology develops, components of an engine are exposed to more severe operating conditions. Operating conditions may include higher power density engines, use of turbo chargers, use of alternative fuels and the like. Under many severe operating conditions, wear and/or oxidation of lubricant and components occurs more readily.
U.S. Pat. No. 4,840,741 discloses antiwear additives derived from pyridines, pyrimidines, pryazines, pyridazines and/or fused derivatives thereof. The antiwear agents are also functionalised with at least one member of the group consisting of halogens, chloromethyl, dichloromethyl, trichloro-methyl, chlorobromomethyl, bromomethyl, dibromomethyl, cyano, isocyano, methylcyano, cyanomethyl, cyanate, isocyanate, thiocyanate, isothiocyanate, nitro, nitromethyl, nitroso, formyl, acetyl, methyl carboxylate, methoxy, methylthio, thiol, and disulphide.
SU 1068466 discloses lubricating oils with good anti-seize and antiwear properties contains 1-4 weight percent of a salt of 1-(2-aminoethyl)-2-imidazolidinone with a di-C8-10-alkyl dithio phosphate.